A turbomachine fan comprises a disk carrying fan blades at its outer periphery, these blades having roots that are engaged in substantially axial grooves in the outer periphery of the disk. The fan blades are held radially on the disk by co-operation between the shapes of their roots and of the disk grooves, the blade roots being of the dovetail type, for example. Inter-blade platforms are mounted on the disk between the fan blades.
In the present technique, the blades are held axially on the disk in the upstream direction by means that are mounted on the disk both upstream and downstream from the blades, thereby preventing the blade roots from moving axially in the disk grooves.
The retaining means situated downstream from the blades comprise at least one hook that is engaged in notches machined in the downstream end portions of the blade roots.
The retaining means situated upstream comprise a ring and an annular web that are fitted on the upstream end of the disk and fastened thereto. The ring is mounted coaxially on the disk and includes a scalloped portion co-operating with a corresponding scalloped portion of the disk. The web is mounted coaxially on the disk to block the ring axially on the disk. The outer periphery of the web bears axially against the blade roots so as to retain them axially in the upstream direction, the inner periphery thereof being pressed against a corresponding annular flange of the disk and being fastened thereto. The outer periphery of the web further includes pegs fastening the upstream ends of the inter-blade platforms.
An annular spinner of substantially frustoconical shape is mounted on the disk, upstream from the blades, and it defines the inside of the annular passage for air entry into the turbomachine. In the vicinity of its downstream end, the spinner has a radially inner flange that is pressed axially against the above-mentioned web and that is fastened to the web on the flange of the disk by screw-and-nut type means.
In the fortunately relatively rare circumstance of a fan blade being lost or broken, the blade strikes against an adjacent fan blade, which is then subjected to a very violent axial force in the upstream direction. The means for retaining the fan blades axially are designed to damp at least a fraction of this axial force by presenting “double flexibility” that enables the other blades of the fan to be retained axially.
The first flexibility is provided by the upstream retaining means that are designed to deform plastically under the effect of the above-mentioned axial force. The second flexibility is formed by the downstream retaining means that are designed to come into abutment against the downstream ends of the blade roots when the plastic deformation of the upstream retaining means has reached a certain threshold. This double flexibility is essential to enable the parts of the fan to hold together in the event of a blade being lost or broken.
Nevertheless, the means that provide this double flexibility present drawbacks, since they comprise a large number of parts: a ring, a web, and the spinner having a flange that is used for fastening the web to the disk, for the upstream retaining means; and a hook co-operating with notches in the blade root for the downstream retaining means. Furthermore, they are bulky and cannot be mounted on a fan of small diameter. The technology for fastening inter-blade platforms to the disk by means of pegs provided on the web is likewise not possible for lack of space in a fan of small diameter. Furthermore, the blade roots need to be machined at their downstream ends in order to form the notches therein for co-operating with the downstream hooks. The materials that can be used for the fan blade are therefore restricted to materials that can be machined.
Finally, on certain turbomachine engines such as test engines, the fan is fitted with a remote measurement system that comprises a sheath extending axially inside the fan disk and including at its upstream end an annular flange for fastening to the disk flange. It is then no longer possible to fasten the spinner flange to said disk flange.